In postgres I have a table with a varchar column. The data is supposed to be integers and I need it in iteger type in a query. Some values are empty strings.
SELECT myfield::integer FROM mytable
ERROR: invalid input syntax for integer: ""
I was just wrestling with a similar problem myself, but didn't want the overhead of a function. I came up with the following query:
SELECT myfield::integer FROM mytable WHERE myfield ~ E'^\\d+$';
Postgres shortcuts its conditionals, so you shouldn't get any non-integers hitting your ::integer cast. It also handles NULL values (they won't match the regexp).
If you want zeros instead of not selecting, then a CASE statement should work:
SELECT CASE WHEN myfield~E'^\\d+$' THEN myfield::integer ELSE 0 END FROM mytable;